The health of an economy cannot be separated from that of its natural support systems. More than half the world’s people depend directly on croplands, rangelands, forests, and fisheries for their livelihoods. Many more depend on forest product industries, leather goods industries, cotton and woolen textile industries, and food processing for their jobs.

A strategy for eradicating poverty will not succeed if an economy’s environmental support systems are collapsing. If croplands are eroding and harvests are shrinking, if water tables are falling and wells are going dry, if rangelands are turning to desert and livestock are dying, if fisheries are collapsing, if forests are shrinking, and if rising temperatures are scorching crops, a poverty-eradication program—no matter how carefully crafted and well implemented—will not succeed.

Restoring the earth will take an enormous international effort, one even larger and more demanding than the often-cited Marshall Plan that helped rebuild war-torn Europe and Japan. And such an initiative must be undertaken at wartime speed lest environmental deterioration translate into economic decline, just as it did for earlier civilizations that violated nature’s thresholds and ignored its deadlines.

We can roughly estimate how much it will cost to reforest the earth, protect the earth’s topsoil, restore rangelands and fisheries, stabilize water tables, and protect biological diversity. Where data and information are lacking, we fill in with assumptions. The goal is not to have a set of precise numbers, but a set of reasonable estimates for an earth restoration budget.

In calculating the cost of reforestation, the focus is on developing countries since forested area is already expanding in the northern hemisphere’s industrial countries. Meeting the growing fuelwood demand in these countries will require an estimated 55 million additional hectares of forested area. Anchoring soils and restoring hydrological stability would require roughly another 100 million hectares located in thousands of watersheds in developing countries. Recognizing some overlap between these two, we will reduce the 155 million total to 150 million hectares. Beyond this, an additional 30 million hectares will be needed to produce lumber, paper, and other forest products.

Only a small share of this tree planting will likely come from plantations. Much of the planting will be on the outskirts of villages, along field boundaries, along roads, on small plots of marginal land, and on denuded hillsides.

The big deforestation success story is South Korea, which over the last four decades has reforested its once denuded mountains and hills using locally mobilized labor. Other countries, including China, have tried extensive reforestation but mostly under more arid conditions and with much less success. Turkey has an ambitious NGO-led grassroots reforestation program, relying heavily on volunteer labor. So, too, does Kenya, where women’s groups led by Nobel Peace Prize–winner Wangari Maathai have planted 30 million trees.

If seedlings cost $40 per thousand, as the World Bank estimates, and if the typical planting rate is roughly 2,000 per hectare, then seedlings cost $80 per hectare. Labor costs for planting trees are high, but since much of the labor for planting these trees would consist of locally mobilized volunteers, we are assuming a total of $400 per hectare, including both seedlings and labor. With a total of 150 million hectares to be planted over the next decade, this will come to roughly 15 million hectares per year at $400 each for a total annual expenditure of $6 billion.

Conserving the earth’s topsoil by reducing erosion to the rate of new soil formation or below involves two principal steps. One is to retire the highly erodible land that cannot sustain cultivation—the estimated one tenth of the world’s cropland that accounts for perhaps half of all erosion. For the United States, that has meant retiring 14 million hectares (nearly 35 million acres), at a cost of close to $50 per acre or $125 per hectare, for a total annual cost approaching $2 billion.

The second initiative consists of adopting conservation practices on the remaining land that is subject to excessive erosion—that is, erosion that exceeds the natural rate of new soil formation. The initiative includes incentives to encourage farmers to adopt conservation practices such as contour farming, strip cropping, and, increasingly, minimum-till or no-till farming. These expenditures in the United States total roughly $1 billion per year.

In expanding these estimates to cover the world, it is assumed that roughly 10 percent of the world’s cropland is highly erodible and should be planted to grass or trees before the topsoil is lost and it becomes barren land. In both the United States and China, the two leading food-producing countries, which account for a third of the world grain harvest, the official goal is to retire one tenth of all cropland. In Europe, it likely would be somewhat less than 10 percent, but in Africa and the Andean countries it could be substantially higher than that. For the world as a whole, converting 10 percent of cropland that is highly erodible to grass or trees seems a reasonable goal. Since this costs roughly $2 billion in the United States, which represents one eighth of the world cropland area, the total for the world would be roughly $16 billion annually.

Assuming that the need for erosion control practices for the rest of the world is similar to that in the United States, we again multiply the U.S. expenditure by eight to get a total of $8 billion for the world as a whole. The two components together—$16 billion for retiring highly erodible land and $8 billion for adopting conservation practices—give an annual total for the world of $24 billion.

For cost data on rangeland protection and restoration, we turn to the United Nations Plan of Action to Combat Desertification. This plan, which focuses on the world’s dryland regions, containing nearly 90 percent of all rangeland, estimates that it would cost roughly $183 billion over a 20-year restoration period—or $9 billion per year. The key restoration measures include improved rangeland management, financial incentives to eliminate overstocking, and revegetation with appropriate rest periods, when grazing would be banned.

This is a costly undertaking, but every dollar invested in rangeland restoration yields a return of $2.50 in income from the increased productivity of the rangeland ecosystem. From a societal point of view, countries with large pastoral populations, where the rangeland deterioration is concentrated, are invariably among the world’s poorest. The alternative to action—ignoring the deterioration—brings not only a loss of land productivity, but a loss of livelihood and ultimately millions of refugees, some migrating to nearby cities and others moving to other countries.

The restoration of oceanic fisheries centers primarily on the establishment of a worldwide network of marine reserves, which would cover roughly 30 percent of the ocean’s surface. For this exercise we use detailed calculations by the Conservation Biology Group at Cambridge University. Their estimated range of expenditures centers on $13 billion per year.

For wildlife protection, the bill is somewhat higher. The World Parks Congress estimates that the annual shortfall in funding needed to manage and to protect existing areas designated as parks comes to roughly $25 billion a year. Additional areas needed, including those encompassing the biologically diverse hotspots not yet included in designated parks, would cost perhaps another $6 billion a year, yielding a total of $31 billion.

There is one activity, stabilizing water tables, where we do not have an estimate, only a guess. The key to stabilizing water tables is raising water productivity, and for this we have the experience gained beginning a half-century ago when the world started to systematically raise land productivity. The elements needed in a comparable water model are research to develop more water-efficient irrigation practices and technologies, the dissemination of these research findings to farmers, and economic incentives that encourage farmers to adopt and use these improved irrigation practices and technologies.

In some countries, the capital needed to fund a program to raise water productivity can come from cancelling the subsidies that now often encourage the wasteful use of irrigation water. Sometimes these are power subsidies, as they are in India; other times they are subsidies that provide water at prices well below costs, as happens in the United States. In terms of additional resources needed worldwide, including the economic incentives for farmers to use more water-efficient practices and technologies, we assume it will take additional expenditures of $10 billion.

Altogether, restoring the earth will require additional expenditures of $93 billion per year. Many will ask, Can the world afford this? But the only appropriate question is, Can the world afford to not make these investments?